Control system for roll grinders

ABSTRACT

A control system for roll grinders of a milling apparatus which effects movement of the grinders away from and toward the grinding bed in accordance with sensed flow of material in order to minimize the power requirements of the mill driving means.

United States Patent Inventor Peter Gauer Kamper Weg 98. Dusseldorf. Eller. Germany Appl. No. 801,032

Filed Feb. 20, I969 Patented July 6, I071 CONTROL SYSTEM FOR ROLL GRINDERS 3 Claims, 3 Drawing Figs.

US. Cl 241/37, 241/ 121 Int. Cl ..B02c 15/00, B02c 25/00 Field ofSearch 241/37,

[56] References Cited UNITED STATES PATENTS 2,696,351 12/1954 Woody 241/37 2909330 10/1959 Hardinge.... 241/121 X 337L872 3/1968 Ronceray 241/132 FOREIGN PATENTS 943,450 12/1963 Great Britain 241/121 Primary Examiner-Donald G. Kelly Attorney-Fannie, Edmonds, Morton, Taylor and Adams ABSTRACT: A control system for roll grinders of a milling apparatus which effects movement of the grinders away from and toward the grinding bed in accordance with sensed flow of material in order to minimize the power requirements of the mill driving means.

CONTROL SYSTEM FOR ROLL GRINDERS BACKGROUND OF THE INVENTION This invention relates to roll grinders and more particularly to a control system for such grinders where it is necessary to interrupt the operation of the mill by starting and stopping.

It has been found by practical experience that in the operation of roll grinders power surge requirements occur if the feed of material to be ground is interrupted or if the mill itself is shut down and restarted. Difficulties arise if in the beginning of the grinding operation the material that is to be ground does not arrive continuously below the grinding rolls but instead arrives in uneven quantities. This results in considerable fluctuations of the driving torque power requirement and simultaneously will produce perpendicular movements of the grinding rolls. These two phenomena lead to thrustlike loads upon the milling system and will cause the constructional elements to be in frictional connection with the energy of the grinding rolls. This problem ordinarily would require construction of the various affected parts much more heavily and expensively than would be necessary if only a medium stress were encountered as in the case of consistent, uninterrupted full load operation of the mill.

Another possibility would be to simply stop the mill (grinder) right in its full load operation and to start it again in its filled state. However, for starting a filled mill, a very high torque is required, particularly after several hours of stoppage, which torque surpasses 2% times the full load torque. In the case of this type of operation, one would require overly large or special motors with a very high starting momentum. In the case of switching on such motors, the electric grid is put under such a strain that the direct switching on in many instances is not permitted. Consequently, additional electric and/or mechanical starting aids are necessary.

Experiments have now shown that the above-mentioned disadvantages can be eliminated if upon starting and stopping the mill a very definite sequence is maintained. If a mill is started up for the first time, then there is no material to be ground yet in the mill on the grinding bed. The same condition prevails if the mill is started up immediately after a full inspection of the mill has taken place. Since, as previously mentioned, during startup the feed material arrives in irregular quantities, it will be advantageous to have the roll grinders come into contact with the feed only after a predetermined uninterrupted supply has been established, and it is further desirable that interruption of feed material will automatically cause cessation of the grinding action by removal of the roll grinders. Consequently, the invention for the stopping and starting of roll grinders is characterized by the fact that, after stopping the supply of material to be ground, the grinding rolls are lifted from the grinding bed by the use of fluid pressure, then the mill is stopped and finally the fluid pressure is cut off, while in the case of starting, one proceeds in the reverse sequence.

been provided. The task of this installation consists in operating at first with a large and later with a smaller capacity, because the pressure requirement of the system will increase steadily on account of increasing spring tension of the roll grinders.

The design of the spring roll grinder, which is known per se, was adapted specially to the control system of the invention. Accordingly, the disclosed spring roll grinder is controlled by movement of swiveling levers which extend upwardly beyond the spring axis. A release cylinder has been provided at the upper end of each-swiveling lever, such cylinder being supplied with fluid pressure via a controlled system and in dependence on the supply of goods to be ground. In a second embodiment presented by way of example herein the operation of a roll grinder is in conjunction with a hydropneumatic spring system. In the case of this embodiment, the contact pressure of the rolls or the position of the grinding rolls is controlled via hydraulic cylinders, which will lift the swinging Moreover, this special sequence will prevent the material that is to be ground, which is on the grinding plate and which is subject to the centrifugal force when the mill is running, from exiting from the mill.

According to the invention, a spring biased roll grinder is provided and control means therefor to avoid peak loads of the roll grinder. The control means includes a sensor, adapted to sense the flow of material to be ground, which will turn on pumps in the case of an interrupted supply via an electric control system, which pumps will lift the grinding rolls from the grinding plate via a fluid pressure installation and which keep the grinding rolls in this position until the sensor in the supply of goods to be ground responds to a renewed supply of material and turns the pumps off. In view of this special method of operating a roll grinder, a special circuit in the pump installation has proven advantageous which is a further object of this invention. In the pump installation, a low-pressure and a highpressure pump have been provided. Furthermore, a check valve switched in parallel with the high-pressure pump has levers of the grinding rolls in dependence on the sensor in the supply ofmaterial.

The sensor in the material supply can be made in different ways. The simplest form compressor a strip of sheet metal which is lifted by the material that is to be ground and which is located on the conveyor belt or chute supplying material to the mill and which will operate a limit switch when the supply of material is interrupted. The sensor can also be made in the form of a light or sound barrier or as an auxiliary contact in an electric system of a single roll conveyor type weigher, or of a dosing conveyor type weigher. As an additional safety, the commands for lifting or releasing given to the grinding rolls can also be controlled by auxiliary contacts of the screen of the distributor of the material to be ground, in addition to the sensor control. In this manner lifting or releasing of the grinding rolls will occur even ifthe sensor circuit is disturbed.

The invention will be explained on the basis of a circuit diagram and on the basis of two embodiments of a spring roll grinder given by way of examples.

FIG. I is a schematic presentation of a circuit for the control system according to the invention in connection with two release cylinders for the swiveling levers of a spring roll grinder;

FIG. 2 shows the schematic presentation of a side view of a spring roll grinder with a steel spring system, whereby the swiveling levers, arranged on the outside with the hydraulically, that is, liquid operated release cylinders, are visible;

FIG. 3 shows the schematic presentation of a side view of a roll grinder with hydropncumatic spring system, where the lifting and lowering of the grinding rolls is accomplished via pressure cylinders acting from below.

The circuit diagram represented in FIG. 1 becomes most easily understandable in connection with the embodiment of a spring roll grinder presented in FIG. 2. The numeral 2 in FIG. 2 designates so-called release cylinders, which cause the movement of swinging levers 6 toward and away from the casing of the mill body 1. Release cylinders 2 are supplied with hydraulic pressure via lines 3. The spring system 4, which has been shown schematically in FIG. 2, serves for the creation of spring biasing tension to maintain the grinding rolls 22 in their operative position. The swinging levers 6 can be swung with the grinding rolls 22 around the axes 7.

With reference to FIG. 1, it can be seen that the release cylinders 2 are connected to a hydraulic control system via the lines 3, which installation includes a high-pressure pump 12 and a low-pressure pump 13. On the left-hand side of the control system, there is an electric control box 10 which received input signals via the line 11 from a sensor 9 in this material that is to be ground (see also sensor 32 in FIG. 3). This material may be supplied to mill body 1 by any convenient means such for example as a chute and conveyor belt as shown in FIG. 3. The tank with the hydraulic pressure medium has been designated with 14. After receipt of the electric signal from the sensor in the material that is to be ground, both pumps 12 and 13 are turned on. At first the low-pressure pump I3 operates at a high capacity sending liquid under pressure via check valves and 16 into lines 3 to cause quick out outward movement of both pistons 2 up to a point of contact with the swinging levers 6, in parallel to the high-pressure pump. (See FIG. 2.) The demand pressure in the hydraulic system rises very quickly due to the increased loading produced by compressing spring system 4, as a result of which the check valve 15 will close and the high-pressure pump 12 will continue to drive out the pistons of the pressure cylinder 2 slowly at a low capacity.

In the case of this driving out movement, as can be recognized from FIG. 2, the spring system 4 of the mill remains constantly stressed, so that the pressure in the hydraulic system has to increase steadily. Then, at a certain length of stroke (height of lift) of the rolls and the corresponding pressure, both pumps are turned off by a pressure monitor 17. The rolls 22 will remain in their lifted position, since the pressure oil that has flowed into the pressure cylinders 2 cannot flow back through check valves 15, 16. This state will only be changed whenever material that is to be ground is fed to the mill again and the sensor 9 in the material responds to it. As soon, therefore, as a signal is received from the sensor 9 in the material, the magnetic valve 18 in return line 3' responds to this signal thereby dumping the pressure in line 3, so that the pistons of the release cylinders 2 are pressed back into the starting position through the force of the spring system of the mill and the weight of the grinding rolls.

In the embodiment according to H6. 3, a roll grinder 21 is shown in conjunction with a hydropneumatic system. Piston rods 25 of pressure cylinders 26 act on the swinging levers 23 of the grinding rolls 22, which therefore are swingable around the axes 24. The pressure cylinders 26 are connected at their upper and at their lower ends with a source of fluid pressure (not shown) via the line 29.

Above on the right is the material chute 30, with the material supply conveyor 31 and the material sensor 32. A line 33 leads form the material sensor to the electric control box 34. A signal is transmitted from this electric control box via the line 33 to a system of pumps, such as those shown by way of example in FIG. 1 whenever the sensor 32 signals the interruption of material flow or the subsequent resumption of flow. By means of the pressure cylinders 26, the grinding rolls 22 can be brought into their operative position or lifted from the mill bed. Therefore, pressure fluid may be admitted to the pressure cylinders 26 selectively at either the upper or the lower ends thereof through the lines 27, 28, depending on the desired position of the grinding rolls 22. If the material sensor indicates by way of an electric signal that the supply of material to be ground has been interrupted, it will be understood that lifting of the grinding rolls will occur by pressure being admitted to line 27 from line 29 by means of an electrically operated control valve 27A.

Control valve 27A may be operated in response to a signal from control box 34 either to admit pressure from line 29 to line 27, or to relieve pressure therein when pressure is admitted to the opposite end of cylinders 26 through line 28. Similarly, the admission of fluid pressure or relieving of pressure in line 28 is under the control of valve 28A which in turn is controlled by signals received from control box 34 and line 35.

in this manner the lifting and the lowering of the grinding rolls 22 is controlled in dependence on the supply of material to be ground exactly in the same way as in the case of the embodiment according to FIG. 2, except that the grinders 22 are biased or moved in directions toward and away from the grinding bed or plate by pressure cylinders 26 and the attendant control system therefor.

There are various possibilities of design for the sensor 9 and 32 in the material to be ground, shown only schematically. As the most simple design, one could have a strip of sheet metal, which is lifted up by the material that is to be ground, located on the conveyor belt or chute, and which, thereby, operates the limit switch. The material sensor could also be developed as a light or sound barrier or as an auxiliary contact in the electric system of a single roll conveyor type weigher or of a dosing conveyor type weigher. As an additional safeguard, the command for lifting or lowering of the grinding rolls could be produced by way of auxiliary sensing contact of the screen for the material feeder. In this manner the movements of the grinding rolls would be controlled even if the sensor circuit should not function.

It will be appreciated that the foregoing description of embodiments of the invention has been merely representative and that departures may be made therefrom without departing from the scope of the invention as set forth in the appended claims.

lclaim:

1. Apparatus for the control of a roll grinder having at least one grinding roll adapted to roll upon a grinding plate upon which material to be ground is fed, conveying means to supply said material to said grinding plate, a mill body and means connected to said grinding roll and said mill body to support said roll in relation to said grinding plate, said connecting means comprising a lever pivotally mounted on said mill body and rotatably supporting said grinding roll, spring means to bias said lever in a direction toward the grinding plate, sensing means for sensing the interruption and resumption of the supply of material to said grinding plate, a fluid pressure motor connected to said lever, a fluid pump connected to said motor, said pump being activated by said sensing means to feed pressure fluid to said motor to urge said grinding roll away from said grinding plate when the material supply is interrupted, thus stopping the grinding operation.

2. The apparatus of claim 1 wherein said sensing means, on resumption of the supply of material to said grinding plate, causes a reduction in the pressure in said fluid pressure motor allowing said spring means to operate said lever to return the grinding roll to operative position in relation to the grinding plate, thus again starting the grinding operation.

3. The apparatus of claim 1 which includes a low fluid pressure pump of high capacity and a high-pressure fluid pump of lower capacity arranged in parallel, separate fluid lines leading from said pump to a common pressure line leading to said fluid pressure motor, check valves in each of said separate lines operating to hold pressure in the common line, pressure sensing means in the line leading to the fluid pressure motor for discontinuing operation of both pumps upon achieving a predetermined pressure of a value capable only by said highpressure pump, and a valve in the line leading to the fluid pressure motor responsive to said material supply sensing means to relieve pressure in said line upon said sensing means indicating the resumption of material flow to the grinding plate.

g g' UNITED STATES PATENT OIEFICE CERTIFICATE OF CORR-: ECTION Patent No. 3, 591,094 Dated July 6, 1971 InVentor(s) Peter Gauer 4 It is certified that error appearsfsin the above-identified patent and that said Letters Patent are hereby corrected as shown below:

. Col. Line Reads i Should Read 2 22 form compressor form comprises 2 68 in this material in the material 3 2 quick out outward quick outward 3 37 leads form leads from 4 after line 25 insert the following paragraph which has been omitted from the patent:

It will be understood that cylinders 2 shown in Figs. 1 & 2

and cylinders 26 of Fig. 3 may properly be referred to as fluid pressure motors.

Signed and sealed this 18th day of January 1972.

(SEAL) Attest:

EDWARD M.FLETCHl-QR,JR. ROBERT GOITSCHALK Attesting Officer Acting Commissioner of Patents 

1. Apparatus for the control of a roll grinder having at least one grinding roll adapted to roll upon a grinding plate upon which material to be ground is fed, conveying means to supply said material to said grinding plate, a mill body and means connected to said grinding roll and said mill body to support said roll in relation to said grinding plate, said connecting means comprising a lever pivotally mounted on said mill body and rotatably supporting said grinding roll, spring means to bias said lever in a direction toward the grinding plate, sensing means for sensing the interruption and resumption of the supply of material to said grinding plate, a fluid pressure motor connected to said lever, a fluid pump connected to said motor, said pump being activated by said sensing means to feed pressure fluid to said motor to urge said grinding roll away from said grinding plate when the material supply is interrupted, thus stopping the grinding operation.
 2. The apparatus of claim 1 wherein said sensing means, on resumption of the supply of material to said grinding plate, causes a reduction in the pressure in said fluid pressure motor allowing said spring means to operate said lever to return the grinding roll to operative position in relation to the grinding plate, thus again starting the grinding operation.
 3. The apparatus of claim 1 which includes a low fluid pressure pump of high capacity and a high-pressure fluid pump of lower capacity arranged in parallel, separate fluid lines leading from said pump to a common pressure line leading to said fluid pressure motor, check valves in each of said separate lines operating to hold pressure in the common line, pressure sensing means in the line leadiNg to the fluid pressure motor for discontinuing operation of both pumps upon achieving a predetermined pressure of a value capable only by said high-pressure pump, and a valve in the line leading to the fluid pressure motor responsive to said material supply sensing means to relieve pressure in said line upon said sensing means indicating the resumption of material flow to the grinding plate. 